1. Field of the Invention
The present invention relates to a battery technology, and particularly relates to a technology for extending the life of and improving the reliability of a lead-acid storage battery.
2. Background Art
A lead-acid storage battery is particularly superior in low-temperature characteristics among secondary batteries (storage batteries), and is a secondary battery which balances battery characteristics with cost competitiveness. A lead-acid battery has a heavier weight per unit volume than a lithium secondary battery has, and has had a basic problem with energy density. The causes of the problem are the use of an electrode of lead having a greater specific gravity than that of lithium or the like, and the use of sulfuric acid having a high specific gravity for an electrolytic solution. However, a wound type lead-acid storage battery structured by making the lead electrode as thin as possible to increase an electrode area per unit weight and winding up a negative electrode and a positive electrode while sandwiching a separating film between them is expected to have a high energy density. If a battery is composed of wound up electrodes with a thin film shape, it can be lightweight, possess a large area, and consequently acquire the high energy density.
However, because a current collector in a lead-acid battery is corroded in a working environment of the battery, the thinning of a current collector has basic problems with reliability. Particularly, the intergranular corrosion particularly among corrosions of a positive electrode material and the elongation phenomenon of the current collector due to the corrosion are problems which lead to the failure of the battery. Because corrosion elongation finally leads to troubles such as electric short and the penetration of the current collector through an electrical component, it becomes a basic problem of the current collector in a lead-acid battery particularly employing a reinforced material such as a current collector grid containing calcium Ca, regardless of an industrial battery or an automotive battery.
JP Patent Publication (Kokai) No. 3-261071 discloses a method for inhibiting the corrosion elongation of a positive current collector in a lead-acid storage battery by enhancing a material strength, as a so-called anti-corrosion-elongation measure.